The invention relates to a method of producing hollow articles which are opened toward their axis, are rotationally symmetrical and are symmetrical about a central plane, from polyurethane multi-component reaction materials by the reaction casting method. A core mold is needed during production to generate the cavity and the reaction mixture is fed from the rotational axis via feed channels to the mold cavity. In particular, it is possible to produce pneumatic tires which are made up of differing polyurethane elastomers, for example, with a flexible tread mixture which can also be reinforced, a rigid casing miture which can optionally also be reinforced and a flexible bead mixture.
Vehicle tires made of polyurethane reaction materials consisting of differing reaction systems are known. A separately produced casing composition is cast around it, for example, in another mold having a tread. As the adhesion of the tread to the casing surface is insufficient under dynamic stress in this case, attempts have been made to introduce the tread mixture and to subsequently load in the casing mixture from one side once the tread has solidified. However, since the rear of the tread is inevitably designed cylindrically by the centrifugal process, the lateral transition of the tread which is usually cambered in the casing region can only be achieved if the tire zenith is extremely thick. In this method, it is only possible to work with slightly reactive casing materials since the liquid casing mixture has to be displaced from the feed position past a bead on the rear of the tread to a second bead before the viscosity is allowed to increase. This method of production becomes even more difficult if reinforcing inlays are used since they reduce the cross-sectional area between the rear of the already cast tread and the mold core in the zenith region. In addition to the time required for the tread mixture to solidify, the associated shrinkage of the tread from the mold surface is also disadvantageous for economic production because reaction mixture can enter the gap between the shrunk tread and the mold surface as the casing is cast.
Attempts have been made to insert two additional mixheads on each bead in order to cast the second casing reaction mixture onto a still liquid tread mixture. However, an apparatus of this type is very bulky and rarely used because of the size of the mixheads necessary for the production of passenger vehicle tires. Ventilation through the feed slots on the two beads becomes very difficult and is only possible at a very slow entry speed and thus with partially opened feed channels. Highly reactive materials cannot be processed in this way. The reliability of production and operation is impaired by the double number of matering units, mixheads, pipe and tube lines, distributor and manipulators.